The image shows 3 S7-1200's and 1 WinCC Flex Runtime (running on a PC?). The wifi-client devices would be wifi bridges since the S7-1200's only connect via wired network, so you would need a bridge device between the AP and each of the 2 S7-1200 PLCs.

The wincc flex runtime can connect to one device at a time so having it communicate with just the 1 PLC is a very good thing.

The software necessary to communicate between S7-1200 PLCs is available. However, if you are using a PC to run the wincc flex runtime, you may as well use OPC or modbus/tcp to collect data from the 2 wireless S7-1200's directly. You will have potential problems with power outage and data loss with the S7-1200's if logic and tags are not properly configured.

I don't see any problems with this configuration. S7-1200 at WiFi AP collects all the data and is directly wired with a PC-Runtime via Ethernet. All what you monitor at the PC-Runtime is from the collecting PLC.

So, in my opionen, the collecting PLC is responsible to get all the data and check, if communication is okay and no data were lost. It's normal TCP/IP commuication. It also depends at the Wifi devices, how stable the connection is. With the Siemens intelligent devices Scalance W784-1 (AP) and W744-1 (Client) it shouldn't be a problem.